The human and financial costs of low-back syndromes to our society are overwhelming. The causes of most low-back syndromes are unknown, but it appears that biomechanical factors are involved. Low-back syndromes unquestionably can be aggravated by mechanical means. Detailed, quantitative studies of the involvement of mechanical factors in the aggravation of low-back syndromes are proposed. The specific mechanical factors that aggravate low-back pain, and a delineation of the trunk substructures that are and that are not involved, will be sought. Three types of studies are called for: (1) basic mechanical property data will be acquired from cadaver and animal material; (2) biomechanical analyses of internal forces and stresses will be made in mathematical models; and (3) clinical studies of physical activity performance differences between patients and controls will be conducted.